The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:    3GPP third generation partnership project    CA carrier aggregation    CC component carrier    CDIS co-existence discovery and information server    CE co-existence enabler    CM co-existence manager    CMOCU central multiple operator coordination unit    CN core network    D2D device to device    E-UTRAN evolved universal terrestrial radio access network (also LTE)    eNB evolved Node B (base station of a LTE/LTE-A system)    GWCN gateway core network    HSS home subscription server    ICIC inter-cell interference coordination    ID identity/identifier    ISM industrial, scientific and medical    LTE-A long term evolution advanced    MME mobility management entity    MOCN multi-operator core network    PGW packet gateway    PLMN public land mobile network    RAT radio access technology    SGW serving gateway    TVDB TV database    TVWS TV white space    WLAN wireless local area network
Wireless radio network operators need to enable sufficient data rates for individual users to utilize different and evolving types of services, and to preserve quality of service as the density of users increase. Together this is seen as network capacity, and given the rapid expansion of data volume and service types now available over wireless networks. Maintaining sufficient network capacity is seen to be a critical challenge going forward.
Solutions to increase network capacity can be generalized into two categories: link level and network level. The best link level improvements have in the past decade been centered on coding technology. The Shannon capacity theory provides an upper limit for data rate at a given bandwidth, and so further capacity improvements from the link level perspective are somewhat limited.
Respecting network level capacity improvements, those can be divided into two types of optimizations: size and spectrum. Size optimization includes reducing the cell size, such as in cellular systems such as LTE reducing from the more traditional LTE macro cell to the LTE-A femto cell. Size optimization can also include utilizing other local communication schemes, such as D2D communications which represent still smaller ‘cells’ of communicating D2D devices. Spectrum optimization considers utilizing the available spectrum as efficiently as possible. Cognitive radio is a concept in which users opportunistically exploit ‘holes’ or unused portions of the radio spectrum for their communications, and falls within the spectrum optimization regime.
Cognitive radio is still a very general concept and it is quite difficult to optimize multiple different RATs over multiple frequency bands. This leads to a further division of the spectrum optimization techniques into coordination of multiple operators using the same RAT in the available frequency bands, and coordination of multiple RATs in the available frequency bands. As part of expanding network capacity there is research into utilizing license exempt frequency bands, sometimes termed shared bands or unlicensed spectrum, for regular communications. Therefore the above same or multiple RAT scenarios may be in licensed bands or in license-exempt bands. Examples of license exempt bands include the ISM bands and the TV whitespaces which the U.S Federal Communication Commission is considering making available for direct use by the general public.
The concept of carrier aggregation CA is well established in the wireless communication arts and has been undergoing development for the LTE/LTE-A systems. In CA the whole system bandwidth is carved into multiple component carriers CCs. Specific for LTE/LTE-A, each UE is to be assigned one PCell which remains active and one or more SCells which may or may not be active at any given time, depending on data volume for the UE and traffic conditions in the serving cell. At least one CC in the system is to be backward compatible with UE's which are not capable of CA operation.
The structure of the extension carrier is not yet determined; it may or may not have a control channel region, it may have only an abbreviated control channel region or it may have a full set of channels so as to be backward compatible with LTE Release 8. In any case the structure is under development for LTE Release 11 and some enhancements to the UL may be possible, particularly to better facilitate machine-type communications on such an extension carrier.
FIG. 1 illustrates the general CA concept for LTE/LTE-A. For a given UE there is assigned a PCell which by example is backward-compatible with LTE Release 8/9 UEs (and therefore 20 MHz in bandwidth though the various CCs may be defined by different bandwidths). That same UE may also have in its assigned set SCell#1, SCell#2 and SCell#3, which for completeness SCell#3 is shown as being non-contiguous in frequency with the other CCs. Any number of the SCells or none of them may be active for that UE at any given time, as coordinated with the eNB. Every UE is to have its assigned PCell always active, and so legacy UEs which are not CA-capable will be assigned one backward-compatible CC and no others.
One approach to prevent congestion of cellular core networks due to the ever-increasing volume of wireless data and number of wireless users is to utilize one or more SCells operating in the license-exempt spectrum. UEs operating in such a SCell will still be utilizing the same RAT as is used in the CCs operating in the licensed bands. But even when these multiple UEs operating in the license exempt band are operating with the same RAT, they may be controlled by different operators which interface with different core networks. In the LTE-A system one approach to exploiting the license-exempt band via CA is to have different LTE-A femto cells controlling that SCell and the UEs operating in that license-exempt SCell band. Relevant background in this regard, including an exposition of difficulties in coordinating different core networks, can be seen at a presentation by M-A Phan, H. Wiemann and J. Sachs entitled FLEXIBLE SPECTRUM USAGE—HOW LTE CAN MEET FUTURE CAPACITY DEMANDS (Ericsson Research, Ericsson Eurolab R&D; Aachen Germany; Jul. 8, 2010) and also in a paper by Rui Yang entitled OVERVIEW OF RESEARCH PROJECTS WITH NYU-POLY (InterDigital Communications, LLC; Melville, N.Y.; Nov. 12, 2010).
Currently, national roaming is used as the way for the UE to use resources from different operators on their licensed bands. One major disadvantage of national roaming is that the PLMN ID of the visited network is broadcasted on the air interface, meaning it is not transparent for the subscribers in roaming situation. In practice it is typical that national roaming is used as a way to support geographical split agreements between different operators. Each operator deploys its own network and uses its own spectrum, so in the predominant case of national licenses the whole available spectrum is not used. But where the LTE operators deploy networks on license-exempt bands, they need to co-operate in a tighter way so that the shared spectrum can be utilized in a reasonable and efficient way.
Generally there are two technical solutions for the coordination between different LTE operators on their licensed bands: national roaming and E-UTRAN sharing (for background see 3GPP TS 23.401 v8.6.0 and 3GPP TR 23.251 v8.1.0, respectively). There are also two general approaches for roaming in LTE: home routed traffic and local breakout. These two approaches differ on the location of the PGW, as is shown at FIGS. 2A-B. In the home routed traffic shown at FIG. 2A the PGW 206 is located in the home network 204 as opposed to the visited network 202. The visited network 202 serves as the CN (EPC) 202 for the visiting UE 20 operating under an eNB 22 in the E-UTRAN radio network. Thus in FIG. 2A traffic from the subscriber 20 is routed by the SGW 212 up to the home network 206. In the local breakout shown at FIG. 2B the PGW 206 is located in the visited network 202 as opposed to the home network 204. In this case traffic from the subscriber UE 20 is routed from the eNB 22 and through the SGW 212 locally to the PGW 206 at the level of the visited network 202. In both approaches the HSS 208 is located in the home network 204, and has the roaming agreements with the MME 210 at visited network.
E-UTRAN sharing means the eNB is shared by different operators. E-UTRAN sharing also has two main approaches as shown at FIG. 2C: MOCN and GWCN. In the MOCN approach at the left side of FIG. 2C the shared E-UTRAN (represented by multiple eNBs 22) is connected to several CNs 202a, 202b via the S1 interface. Each mobile network operator has its own EPC, and so the MME, the SGW and the PGW are not shared and are located in the different CNs 202a, 202b. In this case, the load balance is possible between MME and SGW of a given CN 202a, 202b. In the GWCN approach at the right side of FIG. 2C, the MME is also shared between the different mobile network operators and so there are shown multiple MMEs 210a, 210b, 210c. In current practice the roaming and E-UTRAN sharing are mainly used for the operators within their own licensed bands.
In addition to the LTE approaches shown at FIGS. 2A-C, an IEEE working group under IEEE 802.19.1 has been investigating a more general concept for network sharing, shown diagrammatically at FIG. 3 which is roughly reproduced from FIG. 2 of document IEEE 802.19-10/0055r3 (March 2010; entitled IEEE P802.19 WIRELESS COEXISTENCE). In this architecture there is a central control unit having functions of a coexistence manager CM 302, a gateway/server unit having functions of a coexistence enabler CE 304, and a storage unit which functions as a coexistence discovery and information server CDIS 306. The CM 302 and/or the CDIS 306 can interface with a TV whitespace database 308 to find where there have been reports of available spectrum in the license-exempt band, and the CE 304 interfaces with the UEs 20 which operate in the license-exempt bands. The CE 304 is therefore used as a gateway, including providing responses for the registration and translation. The CM 302 is the main control unit to design and process coordination algorithms and functions. The CDIS 306 is the storage unit to save and provide necessary users data. The coexistence architecture of FIG. 3 has been proposed for the coexistence of different IEEE 802 types of wireless applications.